What Is Semiconductor Doping?

December 15, 2021

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Since silicon wafer manufacturers rarely use pure silicon as semiconductors, they add controlled quantities of impurities to the substrates via the doping process to produce usable semiconductors. This method alters the wafer’s conductor ability as it transforms an intrinsic material into an extrinsic one.

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A Closer Look at Semiconductor Doping

What Exactly Is Doping?

Since silicon has four electrons in its outer orbital that can form perfect covalent bonds with four other atoms, the element can create a framework for crystal structures. Although this crystalline structure looks metallic, silicon crystals aren’t metals. For this reason, only a tiny amount of electricity flows through it.

However, all this can be dramatically changed by forming p- and n-type semiconductors through the process of doping silicon. The doping process involves the intentional introduction of impurities into an intrinsic semiconductor. A chemical reaction that occurs during the process enables impurities to form ionic bonds with silicon atoms in its crystal.

Doping essentially modifies silicon’s structural, electrical, and optical properties. Pure intrinsic semiconductors that have undergone doping are then transformed into extrinsic semiconductors.

What Are N-Type and P-Type Semiconductors?

The two types of impurities introduced into the pure and undoped silicon semiconductor include n-type and p-type.  

The n-type doping involves incorporating small quantities of arsenic or phosphorus into the silicon. Both elements seamlessly get into the crystalline silicon structure because each has five electrons in its outer orbitals. The fifth electron allows an electric current to flow through the semiconductor because it has nothing to bond to, and it’s free to move around.

Alternatively, p-type doping uses boron or gallium as the dopant. Since both elements have three electrons in their outer orbitals, they form holes when mixed into the silicon framework. As a result, the electrons become more mobile, and the holes they create will move in the opposite direction of the electrons' movement.

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